Our ultimate goal is to cure diabetes mellitus by allogeneic islet transplantation. Almost all clinical attempts at allogeneic islet transplants have so far failed, and most have exhibited primary non- function (PNF) without even a transient period of normoglycemia. We have developed a murine of PNF in which disproportionate frequencies of PNF occur in reciprocal islet allograft transplants between B10.BR and C57BL/6 strains. In this mouse model, PNF can be abolished by administration of the anti-macrophage agent, silica, and reduced by administration of either cyclosporine, 15-deoxyspergualin, or larger islet mass. Of note, use of 15-deoxyspergualin was observed to decrease PNF in murine isografts, implying that PNF may be non-specific in nature. Others have found that the cytokines (IL)-1, IL-6, interferon (IFN)-gamma, and tumor necrosis factor (TNF) inhibit beta cell function in vitro. Thus we hypothesize that macrophages or other immunologically competent cells are detrimental to beta cell function by lieu of cytokines generated in a non-specific inflammatory response, which may, in the case of allografts, be augmented by an alloimmune response. We will test the effect of the administration of anti-macrophage agents and specific inhibitors of cytokines on PNF in the mouse islet transplant model. We will also measure cytokine concentrations and evaluate cellular infiltrates in islet grafts at various intervals after transplantation with comparison between allografts and isografts in order to correlate the levels or cell types with the occurrence of PNF. Finally, we will determine whether the cytokines identified as deleterious to islets in vivo directly affect beta cell function or do so by amplification of other components of the inflammatory response. The effect of the cytokines on beta cell function will be tested in vitro for their ability to suppress stimulated insulin secretion. It is expected that data from the proposed experiments in mice will help to form the basis of a rational approach to treatment or prevention of PNF in human islet transplantation. We speculate that reduction of PNF may allow a more efficient engraftment and improved function of transplanted islets, which may obviate the current clinically wasteful approach of using more than one donor pancreas for human islet isolation and transplantation.